1. Field of the Invention
The present invention relates to an information recording medium including a pair of tape reels, a case main body for rotatably accommodating the tape reels, and a reel brake for regulating the rotation of the tape reels.
2. Description of the Related Art
The tape cartridge disclosed in Japanese Laid-Open Patent Publication No 2000-137971 is known as this type of the information recording medium. The tape cartridge includes a pair of reels around which a magnetic tape is wound, a shell, a rid (front cover), a slide shutter, a reel lock member, and a reel lock spring. The shell is composed of an upper half and a lower half and rotatably accommodate the respective reels, the rid is turnably attached to the front end surface of the shell and opens and closes a tape drawing-out pocket portion of the shell, the slide shutter opens and closes the bottom of the pocket portion, the reel lock member locks and unlocks the respective reels in association with the open/close operation of the rid, and the reel lock spring urges the reel lock member.
As a result of examination of the conventional tape cartridge, the inventors have found the following problems. That is, in a drive unit for driving this type of the tape cartridge, detection light is irradiated to the magnetic tape in the tape cartridge, and the tape ends of the magnetic tape are detected thereby. Accordingly, in this type of the tape cartridge, light entering holes for causing the detection light to enter the inside of the shell and light outgoing holes for causing the detection light to outgo to the outside of the shell are formed to the side walls of the shell. In this case, in this type of the tape cartridge, arms of the reel lock member, which is engaged with the rid, are disposed below both the holes so that the detection light, which enters and outgoes through both the holes is not cut off by the arms. Thus, when the rid is turned, the arms are engaged with the rid at the extreme ends thereof at positions far from the axis of rotation of the rid to thereby slide the reel lock member. In this case, the torque of the rid, which is necessary to slide the reel lock member against the urging force of the reel lock spring, increases with a longer distance from the axis of rotation of the rid to the positions where the arms are engaged with the rid. Accordingly, in the tape cartridge described above, it is difficult to smoothly open and close the rid due to the long distance from the axis of rotation of the rid to the positions where the arms are engaged with the rid. In contrast, when a shell having holes formed to side walls is injection molded, a slide metal mold having a slide core must be used. In this case, the manufacturing cost of the slide metal mold is more expensive than that of an ordinary metal mold having no slide core because the slide metal mold has a complex structure. As a result, it is difficult to reduce the manufacturing cost of the tape cartridge described above due to the expensive manufacturing cost of the metal mold.